Tubulin, a subunit of microtubules, is subjected to specific enzymatic post-translational modifications, including cyclic tyrosine removal and addition at the COOH terminus of the alpha-subunit, during normal cellular metabolism. Tubulin is normally tyrosinated in cycling cells. It has previously been shown that de-tyrosinated tubulin accumulates in cancer cells during tumor progression in nude mice. Tubulin de-tyrosination, results from the suppression of tubulin tyrosine ligase and leads to an unbalanced activity of another enzyme, tubulin-carboxypeptidase. Apparently the loss of tyrosinate tubulin represents a strong selective advantage for cancer cells.
The occurrence and significance of tubulin de-tyrosination in human breast tumors has been investigated. Cancer cells with de-tyrosinated tubulin were observed in 53% of the tumors and were predominant in 19.4% of the tumors tested. Tubulin de-tyrosination has also been shown to correlate to a high degree of significance with markers of tumor aggressiveness (Mialhe et al., 2001).
There appears to be three genes described in the literature whose gene products could potentially possess tubulin tyrosine ligase activity, HOLLT (Genbank Accession No. gi|6683745), TTLH_Human (Tubulin tyrosine ligase-like protein; Genbank Accession No. gi|20455371) and TTLL_human (Tubulin tyrosine ligase-like protein 1; Genbank Accession No. gi|20455347; Gene 257 1: 109-117 (2000); Genome Res. 11 (3), 422-435 (2001); and Nature 402 (6761), 489-495 (1999)). The regulation of these genes in normal cells, in addition to transformed cells remains to be determined as does the mechanism of their loss in enzymatic tyrosine-ligase activity during tumor progression. It has been proposed that a reversible phosphorylation event of TTL mediated by a protein kinase may be the basis of TTL loss of function (Idriss, 2001).
Using the above examples, it is clear the availability of a novel cloned tubulin tyrosine ligase protein provides an opportunity for further advancements in the physiological function of tubulin tyrosine ligase proteins, and may be useful for the identification of tubulin tyrosine ligase agonists, or stimulators (which might stimulate and/or bias tubulin tyrosine ligase action), as well as, in the identification of tubulin tyrosine ligase inhibitors. All of which might be therapeutically useful under different circumstances.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of BGS-42 polypeptides or peptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the BGS-42 polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.